This application is related to the co-pending application of Thomas L. Blose, entitled "TUBULAR CONNECTION HAVING A CHEVRON WEDGE THREAD", Application Ser. No. 06/565051, filed concurrently herewith.
The present invention relates generally to a thread form for a tubular connection of the type used in tubing, casing and drill pipe, such as is used in gas and oil wells and, specifically, to such a thread form designed with a parallel chevron thread.
Threaded connections for tubular products such as well casing, tubing and pipe can be designed with so-called "hooked" threads. The load flank or pulling flank of such threads forms a negative or acute angle with respect to the longitudinal axis of the tubular connection and hence flares inwardly in the direction of the adjacent thread root. Such threaded connections are also typically formed on pin and box members which are axially tapered. One problem experienced with prior designs of this type is the inherent tendency of such threaded connections to "catch" or "hang-up" momentarily during disassembly while coming out of a well. During disassembly, the female or box member of the tubular connection is normally facing upward and is held stationary while the male or pin member is unscrewed from the box member and generally provides some degree of tension in the threaded connection during disassembly. If the elevator supports the pin member of the connection vertically without swaying, the box and pin members will easily separate along the vertical axis of the pipe. If, however, the elevator supported pin member of the tubular connection is leaning slightly or, if the support hook is swaying, the disengaged threads of the pin member can be pushed to one side to become partially engaged on one side of the box member.
With standard hooked threads as they now exist in the industry, the pin and box members would become "hung-up" until such time that the axial tension load induced by the derrick elevators became high enough to break the engagement, or until the pin member was jarred radially to disengage the members. In either case, the pin and box members of the pipe joint would then pop or jump apart. The recoil reaction which results upon separation of the pin and box members can cause the disengaging pin end to rebound and impact upon the box member causing damage to the threaded connection.